Production lines have all necessary controls and inspections engineered into them, but an individual building an engine must take responsibility for fits and tolerances. This is the case in a race shop or for a home builder. The basics are in the available manuals for all to see, and you begin, as one man put it, ‘By just getting into it.’ We all begin with just the desire to do it and w willingness to learn from mistakes. Experience causes the unfamiliar to become familiar.
I got a call from two club racers who’d decided to change the crank in their Yamaha, Honda or a Kawasaki. They basically wanted someone to tell them they could do it. They had the manual, some tools, a new crank, and desire. It took them weeks of evenings, and we spoke on the phone often. They found and removed fasteners, pulled the heads and cylinders, and then the pistons.
The parts began to look less scary and more familiar to them. Engine features began to make sense. Each step was in the manual – pulling the ignition rotor and crank primary primary gear. Storing, even labeling, the parts as they came off. They gradually became their own experts. Take an engine assembly clean room for instance. There’s reason for it – modern plain bearings are much more sensitive to airborne dirt than were the ball and roller bearings of the previous era. But a good job can be done in a decently clean shop too, by covering the work when you leave the shop, and by being mindful.
Crankshaft main and rod-journal clearances are set a values known to work, using Plastigage or direct measurement.
Piston-to-cylinder clearances are measured by micrometer and bore gauge. It’s fussy and it’s a skill, but as World War II industries proved, thousands of average men and women learned it routinely. Measure the bore, measure the piston across its skirts, subtract one number from the other, check your work, and that’s the clearance.
At each step, you make verifications like the above and continue with assembly. You install fasteners to specified torque using a torque wrench and the manual. When you have finished you will know the condition and fit of every part. It will be yours.
When I was beginning to learn the basics as a young person, my dad would say to me, ‘What makes you think that when you’re done with all this that thing will run?’